Case tool Relational Database Schema Designer Cai Xinlei Tang Ning Xu Chen Zhang Yichuan CS4221 P06

● Bernstein’s algorithm ● Find closure ● Find all keys ● Check normal form ● Save and load files ● Conclusion ● Demo Overview

Internal Data Structure ● Directed graph e.g. {A->B, AB->C, D->C} Advantages: ● Easy to find closure of a set of attributes ● Easy to eliminate transitive dependencies

Assume the set of attributes in the left/right hand side is represented by X/Y Conditions to be checked: 1.A subset S ⋤ X determines a subset of R ⋤ X with S ∩ R= ∅ e.g. {A->B, AB->C} 1.A subset S ⋤ X determines Y e.g. {A->BCD, AF->BCD} Eliminate Extraneous Attributes

Find Closure 1.Find starting graph node 2.Run bfs to add new attributes to closure 3.Repeat step 2, until no more new attributes can be found Example: ∑ = {A->B, C->D}, find closure of {A, C} {A, C} + = {A, B, C} {A, C} + = {A, B, C, D}

Find Minimum Cover ● Extraneous attributes have been removed in step 1 ● Eliminate all transitive dependencies using previous algorithm

Eliminate Transitive Dependencies 1.Temprarliy delete edge in between X->Y 2.Check reachability X to Y Example: ∑ = {A->B, A->C, B->C}, check A->C

Partition ● Partition by identical left hand side node and its neighbours ● No additional modification on graph

Merge Equivalent Keys ● Find equivalent groups ● Merge equivalent keys on graph ● Print intermediate output

Merge Equivalent Keys

Find All Keys ● Full closure - all the attributes in the relation ● Check if the closure of any combination of attributes is equal to the full closure. e.g. ∑ = {A->B, C->D}. Find {A} +,{B} +,{C} + … {A,B} +, {A,C} +....{A,C,D} +, {B,C,D} + => {A,C} + = {A,B,C,D} ● Before the above step, if there exists a proper subset of attribute that is a key, skip find closure of that combination.

Normal Form Checker ● 1NF ● 2NF ● 3NF ● BCNF

Save and Load File ● Format ● Convenience

Testing ● Unit Testing ● Bernstein’s Algorithm Test ● Test Normal Form Checker and Find Key

Conclusion ● Difficulties encountered ● Lessons learned

Demo